Just purchased my first 5 series (, 1997 model , 67000 miles, manual transmission )and am very pleased with the car but for one problem. Every now and again it will jump out of first gear with a thump - even with a gentle take off . The fault appears to be intermittent. Any answers?

For users in England, I have just had this problem fixed by All Gears in Worksop Notts Telephone Neil on 01909 478581 I dropped the car off and it was ready 3 days later not jumped out of gear since (one month now) used to jump out of first most days! £350 all in Neil said it is the selector forks and a common problem. My car is an E39 520i with 153000 miles on the clock but is driving like new after the fix http.//www.totalbmwmag.co.uk/HandsOn/TechOct.PDF